The invention relates to a conveying and straightening machine adjoining the secondary cooling section of a continuous casting installation for billets of any cross-section, in particular for preforms or blooms of relatively large cross-section and varying billet dimensions, in which case in the straightening region the billet is enclosed on all sides by rollers, whereof the lateral support and guide rollers and preferably the upper straightening and conveying rollers are adjustable in the direction of the billet.
During the continuous casting for example of bars or slabs of steel, a billet is supported and guided by partially driven guide and driving rollers located above and below the billet. In this case, for the casting of continuous slabs it is known (German Patent Specification No. 1 942 782) that a continuous slab is supported on all sides at least in the part of the billet guide directly following the chill mould, whereby the danger of the occurrence of bulging, which is particularly great at this point and thus also longitudinal cracks and ruptures of the billet should be restricted. The lateral rollers provided beside the billet, which are not driven, are adjusted with a predetermined definite force against a fixed measure, which is intended to be sufficient to relieve the load on the billet shell on the wider upper and lower sides.
The casting of billets of greater thickness, in particular of preforms with large billet cross-sections above 200 mm on arcuate continuous casting installations involves special problems, since a plurality of different stresses occur in the billet at the time of straightening the non-solidified preform. The straightening forces are thus applied to the billet by the straightening unit following the billet guide, which unit also operates as a drawing-out unit, by way of the horizontal straightening rollers. In this case, deformations of the billet shell are caused. The deformations are noticeable due to undesirable changes of the cross-section and cracks, which show that it is advisable for the billet to be supported on all sides in the conveying and straightening machine by closed or partially closed roller rims. In the case of bloom or preform installations, this has not been done hitherto and even in continuous slab casting installations, supporting the billet on all sides is known solely directly below the chill mould, which in this case is intended to serve for preventing bulging due to the ferrostatic pressure.
Since, above all, in continuous preform or bloom casting installations, the billet formats change frequently, each adjustment to a different billet dimension thus also necessitates an adjustment of the billet guide including the conveying and straightening machine. If solely upper respectively inner horizontal rollers and lower respectively outer horizontal rollers are present, this measure causes no difficulties. As a rule, the lower respectively outer rollers are attached rigidly to the basic frame of the billet casting installation and the upper respectively inner rollers are moved to the new format by means of hydraulic cylinders, which are located above the billet in the roll stand. However, in the present case, when the billet is supported on all sides, lateral support or guide rollers mounted in the vertical axes of the pairs of rollers are also present and have to be taken into consideration accordingly. These support rollers must also be adapted to the new format.
It proves more difficult that in the case of preform installations, the conditions as regards space are very restricted, since normally two billets lie closely one beside the other. The solution provided by the prior art (German PS No. 1 942 782) for continuous slab casting installations, for the transverse or horizontal displacement of the lateral support rollers, is therefore unsuitable in the case of multiple billet continuous casting installations, because the shifting cylinders arranged horizontally require a very large amount of space, due to which the space-saving incorporation of a second billet located directly beside the latter is no longer possible. An adaptation of the support rollers to different thicknesses of billet is not provided in the known installation.